Telephone system



N. H. SAUNDERS 2,105,012

TELEPHONE SYSTEM Filed Oct. 21, 19755 6 Sheets-Sheet l Jan. 1'1, 1938.

N. AH. SAUNDERS TELEPHONE SYSTEM Jan. 11, 193s.

Filed Oct. 2l, 1955 6 Sheets-Sheet 2 ATTORNEY.

Jan. 11, 1938. N. H. sAUNDERs TELEPHONE SYSTEM Filed Oct. 21, 1935 6Sheets-Sheet 3 INVENTOR. NORMAN H. SAUNDEPS BY f7 ATTORNEY.

N. H. SAUNDERS l* Jan. 11, 1938.

TEpEPHoNE SYSTEM Filed 061.21, 1935 l s sheets-sheet 4 mwsv n. m2 U33INVENTOR. NORMAN H. SAUNDEQS few ATTORNEY.

N. H. SALJMDERSv 2,105,012

TELEPHONE SYSTEM Filed oct. 21, 1935 6 sheets-sheet 5 INVENTOR. NORMANH. SAUNDERS ATTORNEY.

Sm H n j MGM n Il' mm Elm a .MIL g Jan. 11, 1938.

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Jan. 11, 1938. N, H, SA'UNDERS 2,105,012

TELEPHONE SYSTEM Filed Oct. 21, 1935 6 Sheets-Sheet 6 FIG. 6 276 a275360- 36 362- DIAL BACK LINE SWITCH 60/ l 602 r 61/ 'n l.

6/0 /6 HL @ad m- RD. 680 LINE 6/4 Gaaf f v6/2 5.O auf 56 /NcoM/NG TOLL562 LINE SWITCH *4|- in "H 690 LINE z2 56a 654 f :n i

LocAL LNE s/ IETgH s l 65] I E T2 27h A 654 f 7 .M /1 LocAL L". SUB.

l 640 A I HI* I LINE wf :uw

b1'\ L INVENTOR. 561 M -ren SAWSTCH NORMAN H. SAUNDEPS ATTORNEY.

Patented Jan. ll, 1938 UNITED STATES PATENT OFFICE TELEPHONE SYSTEMApplication October 21, 1935, Serial No. 45,845

y Claims. The invention relates in general to telephone systems but moreparticularly to inter-exchange f calls in which an operator is requiredto complete connections between automatic subscribers lines over trunklines connecting two automatic exchanges.

'I'he main object of the invention is the provision of means whereby anautomatic subscriber in one exchange in order to call an automaticsubscriber in another exchange must first call the toil operator over atoll trunk extending from one of the automatic exchanges to the tollexchange, after which the toll operator dials back over this same trunkto operate the automatic switches to complete the desired connection.When such connection is completed the toll operator may disconnect andfree her trunk leaving the connection between the two automaticsubscribers established over one of the trunk lines connecting the twoautomatic exchanges.

One feature of the invention relates to the provision of a monitoringselector operable by'the toll operator to monitor the trunks between thetwo automatic exchanges to determine their idle 01' busy condition.

Other features relate to the circuit renements in the dial back repeaterwhich enables this type of service to be given. l

'Ihe drawings, comprising Figs. 1 to 7, inclusive, show by means of theusual circuit diagrams, a sufiicient amount of apparatus to enable theinvention to be described and understood.

Fig. 1 shows one of thetrunks extending to a distant automatic exchangeterminating in an outgoing repeater and an incoming rotary line switchin the local automatic exchange.

Figs. 2 and 3 show the detail circuits of the novel dial-back repeaterand 3 shows one of the trunks extending to the distant toll switchingcenter.

Fig. 4 shows an all-relay monitor selector for monitoring the trunksconnecting the two automatic exchanges.

Fig. 5 shows one of the local selector switches.

Fig. 6 shows the dial-back, incoming toll, and the local line switches,the usual associated master switches, and one of the local subscriberslines.

Fig 7 shows a one-line diagram of the trunking arrangement in the localautomatic exchange and the trunk lines extending to the distantautomatic exchange and the toll switching center.

Referring now in detail to the drawings, Fig. 1 shows one of the trunksextending to a distant lower windings are opened. Only two trunkreautomatic exchange terminating in an outgoing repeater and an incomingrotary lineswitch. This lineswitch is the well known type of rotarylineswitch which advances its Wipers in response t0 the deenergizationof its stepping magnet. These lineswitches have access to a group ofdial-back repeaters, one of which is shown in Figs. 2 and 3. Theoutgoing repeater comprises a repeating coil RC and five relays, two ofwhich are the usual slow-releasing relays as shown by the cross- 10hatched lower portion. Relay |03 is the Well known shunt fieldelectro-polarized relay having an operating winding and a polarizingwinding.

This relay operates its armature |33 only when the current ilow in theoperating winding is in l5 opposition to the polarizing winding. Therepeaters are accessible from the sixth level of the local selectors,one of which is shown in Fig. 5, and from the monitor selectors, one ofwhich is shown in Fig. 4,

The dial-back repeater shown in Figs. 2 and 3 comprises a group ofrelays and a rotary stepping switch having access to trunk linesextending to the toll switching center. This stepping switch is similarin construction and operation 25 to the well known rotary lineswitchwhich steps its wipers on the deenergization of the stepping magnet. Anumber of the relays are of the usual slow-to-release type as shown bythe crosshatched lower portion and by the copper sleeves 30 over theircores. Relay 206 is a slow-to-operate relay as indicated by thefull-black upper portion. Relays 2|0 and 2l2 are diierential relays andrelay 200 is a shunt iield electro-polarized relay similar to the shuntfield relay |03 in Fig. l. Re- 35 lay 202 has a vibrating spring 220which vibrates upon operation of armature 22| due to the weight 2|9 onspring 220. The weight 2|9 may be adjusted so as to vibrate spring 220for a predetermined time interval after 22| is operated so as 40 tointermittently open and close the circuit to slow-to-operate relay 206.The dial-back repeaters are accessible from the tenth level of the localselectors and from the banks of the incoming rotary lineswitches. Eachdial-back repeater has access to an individual dial-back lineswitch, oneof which is shown in Fig. 6.

Fig. 4 shows the monitor selector comprising a group of relays, two voi.which, 403 and 405, are the slow-to-release type as indicated by thesleeves around their cores, and two two-step relays which close onlytheir .r" contacts on their iirst step and their remaining contacts ontheir second step when the short circuits around their Y the desiredlocal call.

voi? the outgoing repeater in Fig. 1 and is accessible from the .eighthlevel of the local selectors.

Fig. 5 shows one of the local selectors which are of the well knownStrowger vertical and rotary type of switch. These selectors are of therestricted service type having normal post springs which are operatedwhen the Wipers have been raised in a vertical direction opposite therestricted levels. The polarized switching relay 501, as indicated bythe bar through its middle,

is similar infconstruction and operation to the relay disclosed inPatent No. 1,673,884, issued June 19, 1928, to H. C. Pye. The localselectors have access to the dial repeaters, the outgoing repeaters, themonitor selector, reverting call switches, and the local connectors asshown in Fig. 7. These selectors are accessible from the dial back,incoming toll, and local lineswitches shown in Fig. 6.

The lineswitches and master switch shown in Fig. 6 are similar inconstruction and operation to the lineswitch and master switch shown inPatent No. 1,809,086, issued June 9, 1931, to John Voss and B. D.Willis. These lineswitches: have access to the local selectors overtrunk lines such as trunk line 560, 563. Each local subscribers line,one of which is indicated by the circle with A in the center, have alocal restricted lineswitch individual thereto. Each automaticsubscriber,

such as A, is equipped with the usual transmitter, receiver, and callingdevice. The dial-back lineswitches are each individual to and accessiblefrom the dial-back repeaters while the incoming toll lineswitches areeach individual to a toll trunk extending to the toll switching center.The dial-back and incoming toll lineswitches are nonrestricted, havingconductors 680 and 690 for accomplishing a purpose to be more fullydescribed hereinafter.

Referring now to Fig. 7, a general description of the operation will nowbe given. When a local subscriber such as A calls, the subscribers locallineswitch plunges and seizes an idle local selector. lIn case of alocal call, subscriber A dials and operates the selector to seize anidle local con` nector which is thereafter operated to complete In caseof a reverting call the calling subscriber dials and operates theselector to select one of the reverting call switches after which thereverting call switches are operated to signal the desired subscriber onhis own line when he hangs up. In case a local subscriber attempts todial the distant automatic exchange direct then the selector is operatedto the restricted level where it automatically rotates to the eleventhposition where the selector cam springs are operated to give the callingsubscriber a busy signal. In order for the local subscriber to beconnected to a subscriber in the distant automatic exchange it isnecessary for such subscriber to dial the selector to the O level toseize an idle dial-back repeater. When the dial-back repeater is seizeda splash of generator is transmitted over one of the idle toll trunks tothe toll switching center. The toll operator answers and when it islearned that a local subscriber desires connection with a distantautomatic subscriber the toll operator unbalances the toil trunk therebycausing the associated dialback lineswitch to plunge and select an idlelocal selector after which the operator dials back over this same trunkto operate the selector to seize an idle outgoing repeater to thedistant automatic exchange. The operator now dials the number of thedistant automatic subscriber and the cutgoing repeater repeats theimpulses over the automatic trunk to cause the automatic switches in thedistant exchange to complete the desired connection. When the calledsubscriber answers the toll operator disconnects from the toll trunk,thereby freeing such toll trunk for other calls while the local anddistant subscribers talk over the established connection.

Incoming calls from the distant automatic exchange to the local exchangecome in over the outgoing repeater causing the incoming rotarylineswitch to select an idle dial-back repeater which then automaticallyselects an idle toll trunk and signals the toll oprator thereover. Inorder to extend the call to a local subscriber the toll operatorunbalances the line thereby causing the associated dial-back lineswitchto seize an idle local selector after which the toll operator dials backover this same toll trunk to operate the local selector and connector tocomplete the call. When the local subscriber 'answers the toll operatordisconnects and frees her toll trunk for use on other calls.

Since the toll operator is disconnected from the established connectionsbetween the local and distant automatic subscribers, a monitor selectoris provided in the local exchange to enable the toll operator todetermine the busy or idle condition of the trunks connecting the localand distant automatic exchanges. In order to monitor these trunks thetoll operator seizes an idle toll trunk thereby causing the incomingtoll lineswitch to select an idle local selector after which the localselector is operated to seize the monitoring selector. The toll operatornow operates the monitor selector to engage with successive automatictrunks to determine their busy or idle condition.

Having given a general description of the operation, a detaileddescription will now be given. For this purpose it will be assumed thata local subscriber, such as subscriber A in Fig. 6, desires to callanother automatic subscriber in the local automatic-exchange. Inresponse to subscriber A removing his receiver a bridge is closed acrossconductors 610 and 61| thereby completing a circuit for theslow-to-operate line relay 640 as follows: from ground by way of springs664, conductor 61|, through the substation loop, conductor 610, springs643, and through the winding of relay 640 to battery. At armature GMline relay 640 at its back contact opens the circuit to the B. C. O.upper winding of relay 64S and at its make contact grounds conductor 672to make this line busy to the local connectors. At armature 642 relay64B completes the circuit through the lower pull-down winding of theplunger coil 646 in case no other line relay in this particular group isin operated position. This circuit may be traced as follows: fromgrounded conductor 666 extending from the master switch through thenormally closed springs controlled by armatures SI2 and 622, frontcontact and armature 642 and through the lower pull-down winding ofplunger coil 646 to battery. In response to the operation of the pulldown Winding, the plunger (not shown) of the lineswitch plunges into thelineswitch bank to close springs 65|, 654, 652, and 853. The pull-downwinding of coil 646 also operates its armatures to open the circuit toline relay 840 at springs 043 and 044 and at springs 545 completes atemporary circuit through the upper B. C. O. winding o! coil 540 asfollows: from ground by way of iront contact and armature 54|, contact545, and through the upper B'. C. O. winding of coil 545 to battery.Since the master switch maintains the plungers of all idle lineswitchesopposite an idle trunk terminating in an idle local selector, vasdescribed in Patent No. 1,809,086, the closure ot springs 55| and 654extends the loop including the calling subscriber's line over conductors550 and 553 and through armatures 525 and 530 and their back contacts tothe upper winding of line relay 505 to battery and through the lowerwinding oi line relay 505 to ground at the normally closed contactscontrolled by armature 5|6.

Line relay 505 immediately energizes over the above traced circuit andat amature 524 completes the energizing circuit for release relay 505 asfollows: from ground by way of armature 521, amature 525 and frontcontact, and through the winding of release relay 505 to battery. Atarmature 525 line relay 505 also prepares the circuit through the upperwinding of polarized switching relay 501. Release relay 505, uponenergizing, at armature 520 grounds conductor 55| by way of the busy key523 to maintain the local lineswitch operated and the calling line busyto local connectors after the line relay 840 in the plunger lineswitchrestores. At armature 522 release relay 505 completes the circuitthrough the lower polarizing winding of switching relay 501 andcompletes an energizingcircuit through the lower winding of series relay504 by way of off normal springs 5H, and at armature 52| opens a pointin the circuit to the release magnet 50| at its back contact and at itsfront contact prepares a circuit for holding the series relay 504 inenergized position during the dialling period and for operating verticalmagnet 502. Y

In the local lineswitch the slow-to-release line relay 540 deenergizesafter ground is returned over connector 55| and which ground extends byway of springs 553 and through springs 545 and armature 54| and backcontact in parallel to the upper winding of coil 545. At armature 542the dee'nergization of line relay 640 again establishes the chaincircuit to the master switch.

Series relay 505 energizes over the previously traced circuit throughits lower winding, and at armature 5|5 disconnects ground andsubstitutes ground through the dial-tone source by way of cam springs5|3. At armature 5|1 relay 505 opens a further point in the circuit tothe release magnet, at armature 5|8 prepares another point in thecircuit for maintaining itself in operated position during the diallingperiod, and at armature 5|0 opens a point in the circuit through therotary magnet 503. Dial tone is now transmitted to the callingsubscriber by way of dial-tone source, cam springs 5|3, armature SI5 andi'ront contact, through the lower winding of line relay 505, backcontact and armature 530, from thence over conductors 553 and 51|through the substation loop back over conductors 510 and 550 and throughthe upper winding of line relay 505 by way of armature 525.

In response to hearing dial tone the calling subscriber now dials theirst digit of the local called subscribers number. Line relay 506iollows the impulses in the dialled digit and in response to itsdeenergization at armature 524 and back contact completes a circuit forenergizing the vertical magnet 502 and for maintaining series from andback relay |04 in operated position as follows: grounded armature 521,armature 524 contact, armature 52| and front contact, armature 5|0, andthrough the vertical magnet 502 and the upper winding of series relay504 in multiple to battery. Vertical magnet 502 is energized in responseto each impulse to step the wipers 540 to 542 one step in a verticaldirection, while series relay 504 due to its slow releasecharacteristics is maintained in operated position over this pulsingcircuitduring the dialling period. At armature 524 line relay 505temporarily opens the circuit through the release relay 505 but therelease relay being of the slow-to-release type maintains its armaturein operated position during the dialling period. On the rst verticalstep of the wipers oil-normal springs 5| 0 prepares a point in thecircuit to the release magnet 50|, on'normal springs 5| opens theoriginalenergizing circuit oi' series relay 504, and oil-normal springs5|2 prepares a point in the circuit to the rotary magnet 503.

Line relay 505 is maintained energized after the dialling period andshortly thereafter series relay 504 deenergizes. At armature 5|6 seriesrelay substitutes direct ground in place of dial tone, at armature 5|1prepares a. point in the circuit to release magnet 50|, and at armature5|9 completes the circuit for operating the rotary magnet 503 asfollows: from grounded armature 521, armature 524 and front contact,off-normal springs SI2, interrupter contacts 5| 5 of magnet 503, backcontact and armature BES. and through the winding of rotary magnet 500*to battery. Rotary magnet 503, upon energizing, steps the wipers onestep for each energlzation and at interrupter springs 5|5 interrupts thecircuit to magnet 503. Rotary magnet 503 due to interrupter springs 5|5operates in the manner of a buzzer stepping the wipers in a rotarydirection until such time as the circuit is completed for the polarizedswitching relay 501. 'I'he local selector is of the type known as thebattery searching type, and therefore the polarized switching relay 501will not energize until the test wiper 54| encounters a bank Contacthaving battery potential thereon, which potential indicates an idle1ocal connector.

As soon as the Atest wiper 54| encounters an idle local connector havingbattery potential on its incoming test conductor a circuit may be tracedfor energizing the polarized switching relay 501 as follows: from groundby way of armature 520, point 532, back contact and spring 53| of thenormal post springs, through the upper winding of relay 501, armature525, test wiper 54|, and engaged bank contact. and over the incomingtest conductor of the idle local connector to negative battery. Sincethe lower electro-polarizingwinding of switching relay 501 was energizedby way of grounded armature 522 of release relay 505 and since the flowof current through its upper winding is in the proper directionpolarized relay 501 now energizes and at armature 521 opens the circuitextending to the rotary magnet 503 to stop the wipers of the selector inengagement with the bank contacts terminating this local connector. Atarmatures 525 and 530 switching relay 501 switches the calling loop fromthe windings of the line relay 505 to the windings of the line relay inthe local connector.

'I'he line and release relays in the local connector energize in thewell known manner and connect ground back over the incoming testconductor, test wiper 54|, armature 529, point 532,

armature 523, and through the lower winding of polarized switching relay501 for maintaining this relay in energized position through its 'lowerwinding alone as long as ground is maintained on testwiper 64|. Thissame ground transmitted back from the local connector also extends frompoint 532 by way of the busy key 523 and conductor 56| for maintainingthe plunger line switch in operated position and for maintaining thecalling line busy to the local connector. line relay 506 deenergizes inresponse to the operation of polarized relay 501, and at armature 524prepares a further point in the circuit to release magnet 50| at itsback contacts, and atitr front contacts opens the circuit to releaserelay 505.4 Slowt'o-release relay 505 at armatures 520 and 522disconnects ground from conductors 56| and the lower winding of relay501 only after ground has been returned from the seized connector. At

armature 52| and back contact release relay 505 Y prepares another pointin the circuit to release magnet 50|.

The local connector is operated in the wellknown manner by the callingsubscriber to com-V plete the desired local connection, the talkingcircuit including the heavy talking conductors.

In case the local subscriber operates the local selector opposite one ofthe restricted levels then the normal post springs operate to switch thecircuit Ior operating the polarized switching relay over the restrictedservice conductor 562 which in this case is not connected in the locallineswitch because the subscribers, such as subscriber A, are restrictedfrom completingV calls on the restricted levels. Assuming now thatsubscriber A has operated the local selector opposite a restricted leveland since no circuit is completed for switching relay 501 the rotarymagnet 503 continues to operate until the wipers of the selector arerotated to their eleventh position of the bank contacts at which timecam springs 5|3 and 5|4 operate. The operation of cam springs 5|4completes a circuit through the lower winding of series relay 504 by wayof front contact and armature 524 and grounded armature 521. At amature5|3 series relay 504 upon energizing opens the circuit to rotary magnet503 and at armature 5|6 connects the busy tone to the calling subscriberas follows: from busy tone source by way of the front contacts and camsprings 5|3, amature 5|6 and front contact, through the lower winding ofline relay 506 and from thence over the calling subscribers loop, aspreviously described.

In response to busy tone the calling subscriber will replace hisreceiver, thereupon opening the circuit of line relay 506 whereupon thelatter relay deenergizes. At armature 524 line relay 506 opens thecircuit to release relay 505 at its front contact and at its backcontact prepares a point in the circuit to the release magnet, and atits front contact also opens the circuit through the lower winding ofseries relay 504, whereupon the latter relay deenergizes. Whenslow-to-release relays 504 and 505 deenergize, a circuit for operatingrelease magnet 50| may be traced as follows: from grounded armature 521,armature 524 and back contact, armature 52| and back contact, armature5|1, off-normal springs 5|0, and through the winding of release magnet50| to battery. By the operation of the release magnet 50|, the wipers540 to 542 inclusive, are returned to their normal position in the wellknown manner, and when the wipers reach their normal position theofi-normal springs 5|0 to 5|2,

inclusive are returned to their normal positions. The cam springs 6|5and 5|4 are also now in normal position. The local selector is releasedin a similar manner at the completion of a local call over the localconnector by the local connector disconnecting ground sent back over theincoming test conductor to test wiper 54| to open the circuitv throughthe lower winding of switching relay 501, whereupon this relaydeenergizes. At

armature 521 relay 501 completes the circuit for release magnet 50|.This ground is likewise disconnected from conductor 56| with the resultthat the holding circuit through the upper winding of coil 646 of thelocal lineswitch is opened causing the armatures of this coil and theplunger to be restored to their normal position. 'I'his ground islikewise removed from conductor 612 so that local subscriber A may becalled over the local connectors.

It will now be assumed that subscriber A desires to call a subscriber inthe distant automatic exchange, and in order to do so subscriber A dialsthe digit 0 to cause the local selector in the same manner' aspreviously described to be `raised opposite the tenth level after whichthe selector rotates step by step in search of an idle dial-backrepeater. Assuming further that the dial-back repeater shown in Figs. 2and 3 is the ilrst idle dial-back repeater, then the circuit forenergizing the polarized switching relay 501 in the local selector maybe traced as follows: from ground -by way of armature 520, restingcontact and spring 53| of the normal post springs, upper operatingwinding of polarized relay 501, armature 625, wiper 54|, conductor |6|,through the lower winding of impedance 201, conductor 26|, normallyclosed springs 334 of the busy key, armature 3|3'and back contact,through the resistance R5 to battery. Polarized switching relay 501energizes over this circuit and at armatures 526 and 530 connects thecalling subscribers loop across the windings of the start and batteryfeed relay 306. This circuit may be traced as follows: from groundthrough the upper winding of relay 306, conductor 266, conductor |62,wiper 542, front contact and-armature 530, conductor 563, contact 654,conductor 61|, through the substation loop, conductor 610, contacts 65|,conductor 560, armature 526 and front contact, wiper 540, conductor |60,conductor 269, and through the lower winding of relay 306 to battery.

Relay 306 energizes over the calling subscribers loop and at armature323 completes a circuit by way of conductor 265, armature 243 and backcontact, conductor 264, through the winding of battery reversing relay30| to battery for energizing relay 30|. At armature 330 relay 306completes the circuit for energizing relays 302 and 304. Relay 304, uponenergizing, at armature 32| prepares a point in the circuit forenergizing switching relay 305, at armatures 322 and 323 prepares acircuit for connecting interrupted generator and ground to one of thetoll switching trunks. Relay 30|, upon energizing over the above tracedcircuit, at armature 3|0 completes a circuit for starting the ringingmachine at its front contact and at its back contact opens the circuitto the all-trunk-busy relay (not shown), and at armatures 3|| and 3|2prepares a reversing circuit to be explained more fully hereinafter.Hold relay 302, upon energizing, at armature 3|3 disconnects the idlebattery potential at its back contacts and at its front contactsubstitutes ground therefor, thereby connecting ground to the incomingtest conductor |6| and test wiper 54| of the local selector to hold thepolarized switching relay 501 in energia position and for maintainingthe local lineswitch in operated position and the calling line busy tolocal connectors. At armature 3H hold relay 302 grounds conductor 262 toenergize the polarizing winding of polar shunt field relay 200, atarmatures 3|5 and 3|6 short circuits test relay 303 in case the testwiper 343 is in engagement with a busy called toll trunk, while atarmature M6 completes a circuit for operating the marginal steppingmagnet 301 in case the toll trunk is busy.

In case the toll trunk engaged by the wipers 300 to 343, inclusive, isbus ground will be present on the test conductor 302 which groundextends by way of wiper 343, normally closed springs controlled byarmature 328, armature 320 and back contact, armature 3|6, normallyclosed springs controlled by armature Eis, conductor 21|,'ar mature 233,conductor 210, interruptor springs 332, and through the winding ofstepping-magnet 301 to battery. A branch of this same circuit extendsfrom ground as previously traced to armature 3| 6 and thence through thewinding of test relay 303, armature 313, conductor 213, to groundedarmature 222, thereby short circuiting the test 'relay 303 to preventits energization when the wiper 303 engages a grounded bank contact. Thestepping magnet 301 energizes over the above-traced circuit andpositions its pawl preparatory to stepping the wipers of the associatedswitch. Near the end of its stroke magnet 301 opens the interruptercontacts 332, thereby opening its own circuit. Stepping magnet 301thereupon deenergizes and steps the wipers one step into engagement withthe next toll trunk. In case the second called trunk is busy ground isagain encountered by test wiper 303 to maintain the test relay 303short-circuited and again operates the stepping magnet 301.

When test wiper 333 encounters a bank contact without ground potentialindicating an idle toll trunk, a circuit may then be traced forenergizing the test relay 303 as follows: from grounded armature 222,conductor 213, armature SIS, through the winding of test relay 303,normally closed springs controlled by armature 3| 9, conductor 21|,armature 235, conductor 210, interrupter springs 332, and through thewinding of marginal stepping relay 301 to battery. Stepping relay 301 ismarginal and will not energize due to the high resistance of relay 303.Relay 303, upon energizing, at armature 3H prepares a circuit throughthe lower winding of switching relay 305, at armature 3|8 connects thering-back circuit to the calling subscriber, at armature 3|9 substitutesthe battery through resistance R1 for the battery through the steppingmagnet 301, at armature 320 grounds test wiper 303 and conductor 362, tomake this trunk line busy to other dial-back repeaters. Test relay 303is now locked in energized position over the following circuit: fromgrounded armature 222, conductor 213, armature 3|5, through the windingof test relay 303, and through the make contact and armature 3 I 9 andresistance R1 to battery.

The ring-back circuit for transmitting ringback tone to the callingsubscriber may be traced as follows: from interrupted generator throughthe multipled contacts and wiper 340, ring-back condenser, armature 3|8,conductor 263, armature 2| 5, normally closed contacts controlled byarmature 2|6, conductor |60, from thence over the heavy talkingconductors and the calling loop, as previously described.

- The circuit for energizing the high resistance winding relay 31| ofthe delayed ground relay group may be traced as follows: from ground byway of the high resistance winding of relay 31|, over common conductor310, annature 32|, front contact and armature 3|1, through the lowerwinding of switching relay 305, through the interrupter springs 332, andthrough the winding of stepping magnet 301 to battery. Due to the highresistance winding of relay 31|, switching relay 305 and stepping magnet301 do not energize over this circuit. Relay 31|, however, energizes andat armature 312 completes a circuit for energizing the A. C. relay 316in case the ringing machine has been started and generator is applied tothe generator lead. When A. C. relay 316 energizes it operates armature315 to close a circuit to the slowtooperate relay 310. After an intervalof time slow-to-operate relay 314 operates its arma.- ture 313 toconnect direct ground to common conductor 310 to operate the switchingrelay 305 and to short circuit the high resistance relay 31|.

The circuit for energizing switching relay 305 may now be traced asfollows: from grounded armature 313, common conductor 310, armature 32|,front contact and armature 3|1, lower winding of switching relay 305,interrupter springs 332, and through the winding of stepping magnet 301to battery. Motor magnet 301 does not energize in series with switchingrelay 305 but the latter relay at armature 325 completes its holdingcircuit independent of ground on the delayedground lead 310. Atarmatures 323 and 33| switching relay 305 connects generator out overthe toll trunk to signal the toll operator at the toll switching centeras follows: from grounded generator through the resistance R6, frontcontact and armature 322, armature 320, wiper 34|, conductor 360, to thetoll center, through the signailing apparatus thereat back overconductor 36|, wiper 342, armature 33|, and armature 323 and frontcontact, to ground. At armature 321 switching relay 305 opens thecircuit to the slowreleasing ring-relay 304, and at armature 328connects direct ground to test wiper 343 to maintain this toll trunkbusy. Ringing relay 304 deenergizes after an interval and at armature32| opens the original energizing circuit of switching relay 305, and atarmature 322 and 323 disconnects ringing current at the front contactsand at the back contacts thereof connects the line and differentialrelays 203 in bridge of the toll trunk. From the foregoing, it will beseen that ringing current has been applied to the toll trunk conductors360 and 36| for an interval in order to operate the signal at theoperators switchboard.

When the toll operator observes the signal and answers the circuit iscompleted for energizing line relay 209 as follows: from ground throughthe lower winding of line relay 209, lower winding oi differential relay2|0, conductor 261, armature 3|| and front contact, resting contact andarmature 322, armature 326, wiper 34 conductor 350, over the bridge atthe toll board back over conductor 35|, wiper 342, armature 33| armature323 and back contact, front contact and armature 3|2, conductor 266,upper winding of differential relay 2| 0, and through the upper windingof relay 209 to battery. Diierential relay 2|0 does not energize overthe above-traced circuit because both windings are equal and oppose eachother, but line relay 209 at armature 239 completes an obvious circuitfor energizing release relay 208. At armature 240 line relay 209prepares a point in the loop and impulsing circuit f of" impedance 201extending to the dial-back switches. Release relay 208, upon energizing,prepares a point in the circuit to series relay 205 at armature 235, atarmature 236 grounds conductor 26| and the incoming test conductor |6|through the lower windings of impedance 201 to maintain the localswitches in operated position. at armature 231 completes a circuitthrough the lower winding of line reversing relay 20| as well aspreparing the locking circuit for tone relay 206, and at armature 239grounds conductor 214 to maintain the test relay 303 in operatedposition. Line reversing relay 20|, upon energizing, at armature 2I3completes the circuit for energizing timing relay 202 at its frontcontact and at its back contact disconnects ground from the ringingmachine start conductor. At armature 2|4 relay 20| connects anotherground circuit through the polarizing winding of the shunt field relay204 from armature 236, ataar'mature 2 I5 opens the ring-back circuittoth' calling subscriber, at amature 2|1 opens the short circuit aroundthe upper winding to permit pay-station tone if connected to conductor|6| to be induced from the lower winding of impedance 201 to the upperwinding of impedance 201 in order to inform the toll operator that apaystation is calling, and at armatures 2|6 and 2 I8 reverses batteryback over conductors and |62 for supervisory or metering purposes to thecalling line. Timing relay 202, upon energizing, operates its armature22| to start the weight on spring 220 vibrating to intermittently closea circuit to slow-to-operate relay 206. Relay 206 is a slow-to-operaterelay and does not immediately operate its armature and therefore doesnot operate until the vibrations of weighted spring 200 decrease inamplitude or remain closed for an interval of time suillcient for theslow-to-operate relay 206 to operate its armature. After an intervalslow-to-operate relay 206 energizes and at armature 233 again shortcircuits the upper winding of impedance 201 to cut off the pay-stationtone if connected to conductor 6| and at armature 234 completes alocking circuit for itself from grounded :armature 231.

The talking circuit between the local calling subscriber and the tolloperator extends over the heavy talking conductors as follows:conductors 610 and 61|, line-switch contacts 65| and 654, conductors 560and 563, armatures 526 and 530 and their front contacts, wipers 540v and542, conductors |60 and |62, armatures 2|8 and 2I6 and their frontcontacts, armatures 23| and 230 and their back contacts, condensers C2and C3, conductors 261 and 266, armatures 3II and 3|2 and their frontcontacts, back contacts and armatures 322 and. 323, armatures 326 and33|, wipers '34| and 342, and by way of the toll trunk conductors 360and 36| to the toll operator. Talking battery for the toll operator isfurnished through the windings of line relay 209, while talking batteryfor the local calling subscriber is furnished through the windings ofthe battery feed relay 306.

When the toll operator receives the information she may extend the callto a distant ofllce, or may call back through the exchange in which thedial-back repeater is located by momentarily unbalancing the toll trunk.It will rst be assumed that the toll operator completes the desired callto a distant office and after conversation is terminated and when thecalling subscriber hangs up the battery feed relay 306 deenergizes andopens the circuit of reversing relay 30| at armature 329 and at amature330 opens the circuit of hold relay 302. Reversing relay 30 I, upondeenergizing, at armatures 3I| and 3|2 reverses battery back over thetoll trunk to give the operator release supervision. Hold relay 302,upon deenergizing, at armature 3|3 disconnects one of the multiplegrounds from the test lead I6I, at armature 3I4 disconnects one of themultiple grounds to the polarizing winding of shunt field relay 204 andat armature 3I5 disconnects grounded amature 222 from the lower terminaloi' test relay 303.

When the toll operator disconnects, the circuit to relays 209 and 2I0are opened whereupon relay 209 deenergizes. At armature 239 relay 209opens the circuit to release relay 208 and momentarily operates theseries relay 205 which is without effect at this time. Release relay208, upon deenergizing, at armature 235 opens the momentarily closedcircuit to series relay 205, armature 236 disconnects ground from testconductor I6I to free the local switches and disconnect ground from thepolarizing winding of the shunt eld relay 204, at armature 231 opens thecircuit of line reversing relay 20| and unlocks relay 206, and atarmature 239 opens the circuit of test relay 303. Line reversing relay20|, upon'deenergizing, at armature 2|1 short circuits the upper windingof impedance 201, at armature 2I3 opens the circuit of timing relay-202and again grounds the all-trunk-busy lead, and at armatures 2 I6 and 2I8restores the normal line connections. Timing relay 202 deenergizes andat armature 22| opens the circuit to tone' relay 206 and tone relay 206,upon deenergizing at armature 233, opens the shunt across the upperwinding of the impedance 201. Test relay 303, upon deenergizing, atarmature 3I1 closes a short circuit around the lower winding ofswitching relay 305 and likewise completes a circuit for energizingstepping magnet 301 as follows: yfrom grounded armature 325,

` armature 3|1 and'back contact, and through the winding of steppingmagnet 301, to battery. Stepping magnet 301, upon energizing, positionsits pawls preparatory to stepping the wiper of the switch, and atinterrupter springs 332 opens the circuit of switching relay 305.Switching relay 305, upon deenergizing, at armature 325 opens thecircuit to stepping magnet 301, at armatures 326 and 33| opens thecircuit to the toll trunk, at armature 328 disconnects ground from wiper343 to free the toll trunk, and at armature 321 prepares a circuit toringing relay 304. Stepping magnet 301 deenergizes and steps the wipers340 to 343, inclusive, one step and closes its interrupter springs 332,thereby again establishing the short circuit around the lower winding ofswitching relay 305. The local switches, such as the local lineswitchand the local selector, release in the same manner as previouslydescribed and all of the relays in the dial-back repeater are now innormal position and can now be used on subsequent calls.

Assuming now that at the time the local subscriber seizes a dial-backrepeater, all of the toll trunks are busy. In this case,all of theconductors,

such as conductor362individual to each toll trunk, wilLbe grounded withthe result that the switch wipers 340 to 343, inclusive, will continueto step until such time as the test wiper 342 engages the normallygrounded all-trunk busy conductor 363 which, in case all the trunks arebusy, is now no longer grounded. Under this condition, when the switchwiper stops in engagement with this 75 aio'ao'is' set of bank contactsthe test relay is energized and busy tone is transmitted to the callingsubscriber. when test wiper 343 encounters the bank contact terminatingconductor 363 from which ground has been removed, then the test relay303 energizes in the same manner as previously described to transmit thebusy tone back to the calling subscriber. 'I'he busy tone circuit may betraced from the busy tone source, wiper 340, tone condenser, armature 3|8, conductor 263, armature 2 I6, normally closed contacts controlled byarmature 2|6, conductor |60, and from thence back over the calling loopto the calling subscriber in the well known manner. When the delayedground is connected to conductor 310, as previously described, switchingrelay 305 energizes and locks and at amature 321 open the circuit torelay 304, whereupon the latter relay deenergizes. When the callingsubscriber hears the busy tone such subscriber will replace hisreceiver, thereby causing the deenergization of relays 306, 30|, and302, and the release Aof the local lineswitch and selector, aspreviously described. Test relay 303 likewise deenergizes to open thebusy tone circuit and to cause the operation of stepping magnet 301which in turn causes the deenergization of switching relay 305, afterwhich stepping magnet 301 deenergizes and steps the wipers one step.

Returning now to the point where the toll operator is signalled and hasanswered, it will now be assumed that the toll operator is to extendthis call back through the local exchange to the distant automaticexchange instead of to an exchange beyond the toll center, as previouslydescribed. At the time the operator has answered it will be rememberedthat the following relays are operated: relays 306, 30|, 302, 303, 305,209, 208, 20|, 202, and 206. The operator after answering the call nowmomentarilygrounds both conductors 360 and 36|. Ground extending overconductor 360 short circuits the lower winding of relays 206 and 2 I0,while ground over the" conductor 36| holds the line relay 209 energizedand causes the operation of differential relay 2I0. Differential relay2I0, upon operating, at armature 20| cornpletes the circuit forenergizing diierential dialback relay 2I2 as follows: from ground by wayof armature 239 and front contact, armature 20|, armature 225, armature264 and back contact, and through the lower winding of differentialdial-back relay 2|2 to battery. At armature 266 relay 2I2 opens afurther point in the circuit to the ringing machine start lead, atarmature 201 prepares a point in the circuit through its upper winding,at armature 208 closes a circuit for maintaining its lower windingenergized and for short circuiting the lower winding of relay 2|I and atarmature 240 closes a loop circuit through the dial-back lineswitch tocause the operation of line relay' SIU thereat. The short circuit aroundthe lower winding of relay 2li and the circuit for maintaining dial-backrelay 2I2 in energized position may be traced as follows: from ground byway of armature 3M, conductor 262,

armature 20B, lower winding of relay 2| I, lower winding of relay 2I2and from thence by way of back contact and armature 244, armatures 225and 24|, and front contact and armature 239.

The circuit for energizing the line relay 6I0 of the dial-backlineswitch may be traced as follows: from ground by way of Springs SI2,conducto'r 215, armature 249, armature 260, righthand operating windingof polarized shunt-eld relay 204, back contact and armature 232,armature 250, conductor 216, springs 6I3 and through the winding of linerelay 6|0 to battery. Polarized shunt-eld relay 204 does not energizeover the above-traced circuit because the current flow in the operatingwinding is in the wrong direction.

'I'he toll operator now disconnects ground from conductors 360 and 36|,whereupon the differential relay 2I0 deenergizes since the short circuitis now removed from its lower winding. Relay 2|0, upon deenergizing, atarmature 24| removes the Short circuit from around the lower winding ofrelay 2| I, whereupon the latter relay energizes in series with thelower winding of dial-back relay 2I2 over the circuit previously traced.Relay 2II, upon energizing, at armature 242 prepares a point in thelocking circuit to switchthrough relay 203, at armature 203 opens thecircuit to trunk reversing relay 30|, at armature 240 opens the originalenergizing circuit through the lower winding of dial-back relay 2|2 atits back contact and at its front contact prepares a point in thecircuit to the upper windings of relays 2H and 2|2, and at armature 245opens a further point in the circuit to the stepping magnet 301. Trunkreversing relay 30| accordingly deenergizes and at armatures SII and 3i2reverses the current back over the toll trunk conductors 360 and 36| toindicate to the toll operator that she may dial.

Returning now to the dial-back lineswitch at a time when the circuit tothe line relay I0 is completed. Relay 6|0, upon energizing, at armatureSI2 completes the circuit for the lower pulldown winding of plunger-coil616 as follows: from ground at the master switch by way of conductor660, front contact and armature 6i 2, and through the lower pull-downwinding of plunger coil Sl to battery. In response to the operation ofthe plunger coil 6|6 the plunger in the dial-back lineswitch is operatedto plunge in on an idle trunk and in this case, assuming that the trunkconductors 560 to 563 extend to another local selector similar to theselector shown in Fig. 5, the plunger will operate and close springs 60|to 600, inclusive. The operation of the plunger coil 6I6 also at springs6I3 and 6I4 opens the circuit to line relay 6|0 and at spring SI5momentarily completes a circuit through the upper winding of coil BIBfrom ground by way of the front contact and armature GII, non-restrictedconnector 680, springs 6 I 5, and through the upper winding of coil 6|6to battery.

In order to avoid duplication of drawings it will be assumed that thelocal selector shown in Fig. is now a different selector than the onetaken into use by the local subscriber, and that in response to theplunging of the dial-back lineswitch the following circuit is completedfor line relay 506 of this local selector as follows: from groundthrough the normally closed springs controlled by armature 5| 6, lowerwinding of line relay 506, back-contact and armature 530, conductor 563,springs 604, conductor 215, armature 209, armature 200, through theright-hand operating winding of polarized shunt-eld relay 204, backcontact and armature 232, armature 250, conductor 216 springs 60|,conductor 560, armature 626 and back contact, and through the upperwinding of line relay 506 to battery. 'I'he operation of the dial-backlineswitch and local selector are similar to that previously describedfor the local lineswitch and local selector used by the calling localsubscriber, and therefore only a brief description of the operationswill be given. Line relay 506, upon energizing, at armature 524completes the circuit for energizing release relay 505 and at armature525 prepares the test circuit for the polarized switching relay 501.Release relay |5, upon energizing, at armature 520 connects ground toconductor 56| to maintain the dial-back lineswitch in operated positionafter the line relay 6|0 deenergizes, at amature 52| prepares a point inthe circuit to a point in the impulsing circuit to the vertical magnet502 and the series relay 504, and at armature 522 closes a circuitthrough the lower polarizing winding of switching relay 501 andcompletes the circuit for operating series relay 504. Series relay 504,upon energizing, at armature 5|6 substitutes ground through thedial-back tone source for ground at thelnormally closed springscontrolled by arma-V ture`5|6 in order to give the operator the dialtone, at armature 5|1 opens a pointin the circuit to the release magnet.at armature 5|3 prepares the circuit for the vertical magnet 502 and atits own upper winding, and at armature 5|9 opens the circuit to therotary magnet 503. Dial tone is now transmitted back to the tolloperator as follows: from grounded dial tone source, back contact andcam spring 5|3, armature 5|6, lower winding of line relay 506, frontcontact and armature 530, conductor 563, springs 604, conductor 215,condenser C, armature 233, condenser C3. conductor 266, and from thenceback over the heavy talking conductors, as previously traced, to thetoll operator.

When the toll operator hears dial tone she then dials the digit requiredto operate this other local selector to seize an idle trunk extending tothe distant automatic exchange and thereafter dials the calledsubscribers number in the distant automatic exchange to complete thedesired connection. In response to the first digit, or in this case thedigit 6, line relay 209 in the dial-back repeater follows the impulsesand deenergizes six times. Each time line relay 209 deenergizes, theloop circuit extending through the line relay 506 in the local' selectoris opened at armature 240, while at armature 239 and its back contact acircuit is completed for energizing the series relay 205 and at thefront contacts of armature 239 the circuit through the release relay 209is momentarily opened but the latter relay, being of the slow-to-releasetype, maintains its armatures attracted throughout the impulsng series.The circuit for energizing series relay 205 may be traced from groundedarmature 239 and back contact, and armatures 235 and 224, through thewinding of series relay 205 to battery. Series relay 205 is also of theslow-to-release type and therefore maintains its armatures attractedthroughout the lmpulsing period. At armatures 230 and 23| relay 205opens the circuit extending back to the calling subscriber to preventthis subscriber from hearing the dial impulses and at armature 232 shortcircuits the right-hand operating winding of the polarized shunt-fieldrelay 204 in order to improve the impulsing circuit. Slow-to-releaserelay 205 falls back after each dialling period. At armature 232 opensthe direct loop to the dial-back switches and closes a loop in serieswith the right-hand operating winding of shunt eld relay 204 and theresistance RI in multiple; at armatures 230 and 23| reconnects thecalling subscriber. The non-inductive resistance R2 prevents completelyopening the loop circuit to the dial-back switches during the transferfrom the direct loop to the loop in series with relay 204. Thenon-inductive resistance RI reaioao duces the impedance of the loop tothe dial-back switches.v l

In the local selector each time relay 506 deenergizes said relay atarmature 524 completes a circuit for operating the vertical magnet 502and for maintaining relay 504 in energized position, as previouslydescribed. The vertical magnet 502 in response to these impulses raisesthe wipers and shaft opposite the sixth level at which time the normalpost springs are operated. The off-normal springs close on the iirstvertical step of the shaft to prepare the circuit for the release magnet50| at olf-normal springs 5|0, to open the original energizing circuitof series relay 504 now held over its upper winding, and at oil-normalsprings 5|2 prepares a point in the circuit for the rotary magnet 503.After the impulsing period the slow-to-release series relay 504deenergizes and at armature 5|6 disconnects dial tone and againreconnects ground. At armature 5|1 relay 504 prepares a point in thecircuit to release magnet 50|, at armature 5|8 opens a point in its owncircuit, and at armature 5|9 completes the circuit for operating therotary magnet 503. Rotary magnet 503, upon energizing, steps the wipersinto engagement with the rst set of bank contacts in the sixth level andat interrupter contacts 5|5 interrupts its own circuit. The rotarymagnet 503 continues to operate in the manner of a buzzer until suchtime as the test wiper 54| finds battery potential on a test contactterminating an idle outgoing repeater to the distant automatic exchange,at which time the circuit for the polarized switching relay 501 iscompleted to stop further rotation of the switch wipers.

Since the local selector has been operated to the restricted level thecircuit for operating the switching relay 501 now includes the operatednormal-post springs and the non-restricted conductor 600 inthe dial-backlineswitch as follows: from ground by way of armature 520, back contactand spring 523 of the busy key, conductor 56|, springs 602,non-restricted conductor 600, springs 603, conductor 562, front contactand spring 53|, of the normal-post springs, upper winding of switchingrelay 501, armature 525, test wiper 54|, conductor |51, nonnally closedsprings controlled by armature I2, armature HJ and back contact,armature |20 and back coni tact, and through the resistance R tobattery. Polarized switching relay 501 very quickly energizes over theabove-traced circuit and at arma.- ture 521 opens the circuit to therotary magnet to prevent further rotary operation of the wipers. Atarmatures 526 and 530 switching relay 501 disconnects the line relay 506and extends the loop from the dial-back repeater to line relay |02 inthe outgoing repeater shown in Fig. 1. At armature 528 relay 501 closesa holding circuit through its lower polarizing winding independent ofground at armature 522 and ground at armature 520, and at armature 529prepares a circuit to hold itself in energized position and maintain thepreceding switches operated when ground is sent back from the repeater.Line relay 506, upon deenergizing, at armature 524 prepares a point inthe circuit to the release magnet 50| and also opens another point inthe circuit to the release relay 505, and at armature 525 opens thecircuit to the upper operating winding of the switching relay 501 whichrelay is now held in operated position through its lower winding alone.Relay 505, being slow to release, does not deenergize until after groundis sent back over conductor |51 from the outgoing repeater at which timethis ground extends by way of wiper 54|, armature 529, and armature 528to hold relay 501 in operated position, and which ground likewiseextends by way of the busy key over conductor 56| to maintain this localselector busy and to hold the dial-back lineswitch in operated position.When release relay 505 deenergizes after an interval, said relay atarmature 520 disconnects ground from conductor 56| now grounded from theoutgoing repeater, at armature 52| prepares a further point in thecircuit to the release magnet 50|, and at armature 522 likewisedisconnects ground from the lower winding of switching relay 501 which,however, is also grounded from the repeater, as previously described.

Line relay |02 in the outgoing repeater is energized over the followingcircuit when the switching relay 501 in the local selector switchesthrough: from ground through the lower winding of line relay |02,through the lower left-hand winding of repeating coil RC, normallyclosed springs controlled by armature conductor |56, wiper 542, frontcontact and armature 530, conductor 553, back through the looppreviously traced through the dial-back lineswitch and dialback repeaterto conductor 560, amature 526 and front contact, wiper 540, conductor|55, normally closed springs controlled by armature 0, through the upperleft-hand winding of repeating coil RC and through the upper winding ofline relay |02 tobattery. At armature H3 line relay |02 completes thecircuit for energizing release relay |04, and at armature ||4 prepares apoint in the loop circuit extending to the distant automatic exchange.Release relay |04, upon energizing, at armature ||5 completes thecircuit through the polarizing right-hand winding of polarized shuntfield relay |03, at armature I6 completes the circuit for energizingswitching relay |05, and at armature ||1 connects ground to conductor|51 by way of the normally closed springs controlled by armature ||2 tomaintain the switching relays 501 in the local selector energized and tomaintain the dial-back lineswitch operated. Switching relay |05, uponenergizing, at armatures ||B and |2| disconnects the rotary incominglineswitch from the outgoing trunk conductors at back contacts and atthe front contacts of these armatures completes the loop circuitext-ending to the distant automatic exchange. At armature 9 relay |05opens a point in the circuit to the reversing relay and at armature |20prepares a substitute circuit for grounding armature I|1 during theinterval when relay |04 is released and relay |05 is falling back.

The loop circuit extending to the distant automatic exchange may betraced from conductor armature I8 and front contact, upper righthandwinding of repeating coil RC, through the operating winding of thepolarized relay |03, lower right-hand winding of repeating coil RC,pulsing armature H4, front contact and arma.- ture |2|, and by way oftrunk conductor |53 to the distant automatic exchange. The closure oithis loop circluit in the distant automatic exchange operates the linerelay therein to prepare the automatic switches for operation. The ow ofcurrent through the operating winding of the polarized shunt field relay|03 is in such a direction that the relay does not operate its armature|33 at this time. The toll operator now dials the digits of the calledsubscribers number field relay in the distant automatic exchange,whereupon line relay 209 in the dial-back repeater at armature 240interrupts the circuit to the line relay |02 in the outgoing repeater,whereupon the line relay |02 at armature ||4 repeats the impulses overthe trunk conductors |5| and |53 to operate the automatic switches inthe distant exchange to complete the desired connection. At arma.- tureI3 line relay 02 intermittently opens the circuit to slow-to-releaserelay |04 but the latter relay, due to its maintained energized duringthe impulsing perod.

When the called party in the distant automatic exchange answers the flowof current is reversed over the trunk conductor 5| and |53 through theoperating winding of polarized shunt |03 to cause this polarized relayto operate its armature |33. At armature |33 relay |03 completes thecircuit for the reversing relay 0|, whereupon the latter relay atarmature 2 connects direct ground to conductor |51 to maintain the localselector and dial-back lineswitch in operated position. At armatures 0and ||I reversing relay |0| reverses battery back over conductor |55 and|56 for operating the shunt eld polarized relay 204, which it will beremembered is included in the loop circuit extending to the dial-backswitches.

The reversal of current through the operating winding of polarized relay204 causes the operation of this relay whereupon at armature 221 acircuit is closed through the winding of switchthrough relay 203 andthrough the upper winding of line reversing relay 20|. At armature 228relay 204 again completes the circuit for energizing trunk reverse relay30| and at armature 229 shorts the resistance R2 at the back contact andarmature 232. At armature 223, relay 203 upon energizing prepares apoint in its own locking circuit, at armature 224 opens the circuit toseries relay 2.05, at armature 225 opens the circuit through the upperwindings of relays 2H and 2 I2, at armature 222 disconnects one of themultiple grounds from the lower terminal of test relay 3|3, at armature225 and back contact removes the resistance R| from in multiple with theoperated winding of relay 204 to improve transmission, and at the frontcontact thereof connects the operating winding of the polarized relay204 directly across the trunk conductors 215 and 216 independent ofarmature 240 to prevent further interruption of the loop to the dialbackswitches when line relay 209 is deenergized. The trunk reversing relay30| is energized over the following circuit: from ground by way ofarmature 329, conductor 255, armature 243 and front contact, armature228, conductor 264, and through the Winding of trunk reversing relay 30|to battery. At armatures 3| and 3I2 trunk reversing relay 30| reversesbattery back over the toll trunk conductors 360 and 36| to give the tolloperator answering supervision in the well known manner.

When the toll operator receives the answering supervision indicatingthat the distant automatic called subscriber has answered, the tolloperator will disconnect by opening the circuit to relays 209 and 2|0.Relay 209 accordingly deenergizes and at armature 239 and front contactopens the circuit to release relay 208. At armature 239 and back contactline relay 209 completes the locking and at armature 240 opens theprevious loop which loop is slow-release characteristics isV now closedthrough armature 225 and front contact. Slow-to-release relay 208, upondeenergizing, at armature 236 removes one of the multiple groundsconnected to conductor |6| and to the polarizing winding of relay 204,at armature 231 opens the locking circuit of tone relay 206 and thecircuit through the lower winding of line reversing relay 20 |v which,however, is maintained in operated position over its upper winding, andat armature 238 opens the circuit to test relay 303. Tone relay 206,upon deenergizing, at armature 233, removes the short circuit from theupper winding of impedance 201. Test relay 303, upon deenergizing, atarmature 3|1 and back contact completes the short circuit around thelower winding of switching relay 305 and also completes the circuit forenergizing stepping magnet 301, as previously described. At armature 3|8relay 303 opens a point in the ring-back circuit, at armature 3|3 opensa point in its own locking circuit as well as preparing the automaticstepping circuit for stepping magnet 301, and at armature 320 preparesanother point in the stepping circuit to stepping magnet 301. Thecircuit for energizing stepping magnet 301 may be traced as follows:from grounded armature 325 and front contact, armature 3|1 and backcontact, and through the winding of stepping magnet 301 to battery.Stepping magnet 301 operates its pawl preparatory to stepping the wipersof the associated switch, and at interruptor springs 332 opens thecircuit through the lower winding of switching magnet 305, as well asopening the short circuit around the lower winding of switching relay305. Relay 305 deenergizes after an interval and at armature 325 opensthe circuit to stepping magnet 301 to allow the stepping magnet todeenergize and step the wipers one step. At armatures 326 and 331 relay305 upon deenergizing opens the circuit extending to the tollk operatorover the toll trunk, at armature 321 again establishes the circuit forenergizing ringing relay 304, and at armature 328 removes ground fromtest wiper 343 and conductor 362 to make this toll trunk available forother calls. The operation of ringing relay 304 is without eiect at thistime because switching relay 305 is not in operated position. Thedial-back repeater is now operatively disconnected from the toll trunkwhich is free to be seized and used on other calls.

The calling local subscriber and the called distant automatic subscribermay now converse over the following talking circuit: from localsubscriber A over conductors 610 and 61|, springs 65| and 654,conductors 560 and 563, through the first local selector by way ofarmatures 526 and 530 and front contacts, wipers 540 and 542, conductors|60 and |62, armatures 2|8 and 215 and their front contacts, armatures23| and 230 and their back contacts, condensers CI and C, back contactand armature 232, and front contact and armatures 250 and 249,conductors 216 and 215, dial-back .line switch contacts 60| and 604, thetalking conductors extending to the second local selector which, in thiscase, we are assuming to be a selector like the local selector in Fig.5, and thence by way of armatures 526 and 530 and their front contacts,wipers 540 and 542, conductors |55 and |56, front contacts and armatures||0 and and through the left-hand windings of the repeating coil RC, andfrom thence through the righthand winding of the repeating coil RC andcondenser, armature ||4, front contacts and armatures I8 and` |2|, andover trunk conductors |5| and |53, and through the automatic switches inthe distant automatic exchange to the called subscriber. Talking batteryto the called subscriber is furnished from the automatic switches in thedistant automatic exchange and talking battery for the local callingsubscriber is furnished through the windings of relay 306.

After conversation and in response to the called automatic subscriberreplacing hisreceiver, the current flow over trunk conductors 15| and|53 is reversed in the well known manner. Due to this reversal ofcurrent in the operating winding of polarized relay |03, relay |03deenergizes and at armature |33 opens the circuit to the reversing relay|0|, whereupon the latter relay at armatures ||0 and reverses batteryback through the operating winding of polarized relay 204. This reversalof current in the operating winding of polarized relay 204 causes thedeenergization of the latter relay.' At armature 221 relay 204disconnects one of the ground connections from the upper winding of linereversing relay 201 and switch-through relay 203 which relays, however,are still maintained energized from ground at armature 239 by way ofarmatures 242 and 223. At armature 228 relay 204 opens the circuit totrunk reversing relay 30| to restore the latter relay to its normalposition, and at armature 229- removes the shunt around armature 232.

When the calling subscriber hangs up the circuit to battery feed relay306 is opened whereupon this relay accordingly deenergizes. At armature330 relay 306 opens the circuit to hold relay 302 and ring relay 304.Relay 302, upon deenergizing, at armature 3|3 again connects theresistance R5 and battery to the release trunk |6| through the lowerwinding of impedance 201 at its back contact and at its front contactremoves one of the multiple grounds from the conductor |6|. At armature3|4 relay 302 disconnects the remaining ground from the release trunkconductor |6| to free the local selector and lineswitch extending to thecalling line, and also opens the circuits to relays 2|| and 2|2 and thepolarizing winding of relay 204. Relay 2|2, upon deenergizing, atarmatures 249 and 250 opens the loop circuit extending to the dial-backswitches to permit the dial-back switches including the dial-backlineswitch and the second local selector to release. Relay 2| l, upondeenergizing, at armature 242 opens the circuit to switch-through relay203 and line reversing relay 20| to cause these relays to deenergize. Atarmature 203 relay 2li prepares the original energizing circuit of relay30|, at armature 233 prepares the original energizing circuit ofdial-back relay 2|2, and at armature 235 prepares a point in thestepping circuit to stepping magnet 301. Switch-through relay 203, upondeenergizing, at armature 223 opens a point in its own locking circuit,at armature 224 prepares a circuit to relay 205, at armature 225 againprepares the circuit for relay 2|2, at armature' 222 grounds conductor213 to prepare the circuit for test relay 303, and at armature 226connects the resistance RI 'in bridge of the operating winding ofpolarized relay 204. Relay 20|, upon deenergizing, at armature 23| againgrounds the all-trunk-busy conductor at its back contact and at itsfront contact opens the circuit to timing relay 202, at armature 2|5prepares a point in the ring-back circuit, at armature 2|1 places ashunt around the upper winding of impedance 201, and at armatures 2|6and 2IB restores the talking conductors to normal position. Timing relay202 upon energizing at armature 22| opens a point in the circuit to tonerelay 206.

The disconnection ofA ground from release conductor 6| by thedeenergization of release relay 302 opens the holding circuit to theswitching relay 501 in the rst local selector and to the plunger coil646 of the local line switch, whereupon the relay and coil deenergize.Relay 501, upon deenergizing, completes the circuit for the releasemagnet 50| to cause the selector to release in the same manner aspreviously described. The ldcenergization of the plunger coil 646 in thelocal lineswitch causes the local lineswitch to restore in the wellknown manner.

When the loop to the dial-back lineswitch is opened at armatures 209 and250 by the deenergization of relay 2|2, relay |02 in the outgoingrepeater deenergizes. Relay |02, upon deenergizing, at armature H3 opensthe circuit of release relay |04 and at armature ||I| opens the loopextending to the distant automatic exchange to release the automaticswitches therein in the well known manner. Release relay |04, upondeenergizing, at armature I5 opens a circuit extending through thepolarizing winding of relay |03, at armature ||5 opens the circuit toswitching relay |05, and at armature i1 substitutes the ground atarmature |20 for the ground at armature |!1 for maintaining the releasetrunk |51 grounded by means of which the second local selector and thedial-back lineswitch is maintained in operated position. Switching relay|05, upon deenergizing, at armatures I |8 and |2| connects the trunkconductors |5| and |53 to the incoming rotary lineswitch, at armature|20 and front contact disconnects ground from release trunk conductor 51to open the circuit to the switching relay in the second local selectorand the plunger coil in the dial-back lineswitch, and at the backcontact connects battery through the resistance R so that the outgoingrepeater may be seized for other outgoing calls.

When ground is disconnected from release trunk conductor |51 the secondlocal selector seized by the dial-back lineswitch and this lineswitchare released by the deenergization of the switching relay, similar toswitching relay 501, and by the deenergization of the plunger coil 6|6.Since the release of the dial-back lineswitch and the second localselector seized by such lineswitch is similar to the release of thelocal lineswitch and the rst local selector, a further description ofthe releasing operation will not be given. All of the apparatus now usedin extending and completing a call between a local calling subscriber toa distant called automatic'subscriber by the aid of the toll operatorare now in normal position and may be used on subsequent calls.

It will now be assumed that an automatic subscriber in the distantautomatic exchange, desires to talk with an automatic subscriber in thelocal exchange. In this case the distant automatic subscriber operatesthe distant automatic switches to seize one of the idle trunks extendingto the local exchange and it will therefore be assumed that the trunkconductors |5| and |53 are the trunk conductors engaged by the distantautomatic switches in initiating this call. When this trunk is seized, abridge is closed across the conductors |5| and |53 at the distantautomatic exchange to complete the energizing circuit for line relay |08of the incoming lineswitch as follows: from ground through the lowerwinding of line relay |08, back contact and armature |24, back contactand armature |2|, trunk conductor |53 through the loop in the distantautomatic exchange to trunk conductor |5|, armature ||8 and backcontact, armature 22 and back contact, and through the upper winding ofline relay |08 to battery. At armature |21 relay |06 completes anenergizing circuit for the stepping magnet |09 from grounded armature I2B and at armature |20 completes the circuit for energizing theslowto-operate relay |01. Stepping magnet |09, upon energizing,positions its pawl preparatory to stepping the wipers of the incomingrotary lincswitch, and at interrupter springs |29 opens a point in itsown automatic stepping circuit. After an interval slow-to-operatc relay|01 energizes and at armature |25 prepares a point in the automaticstepping circuit of magnet |09. At armature |26 and back contact relay|01 opens the circuit to stepping magnet |09 and its front contactprepares a point in the energizing circuit of switching relay |06 andalso completes the circuit for energizing reversing relay by way ofarmature ||9. Reversing relay |0| at armature ||2 connects ground to therelease trunk conductors |52 and |51 to mark this outgoing repeater busyto the monitoring and local selectors. Stepping magnet |09, upondeencrgizing, steps the wipers |30 to |32, inclusive, one step intoengagement with the next set of bank contacts, and at armature |29completes a circuit for energizing switching relay |06 or for shortcircuiting this latter relay dependent upon the idle or busy conditionof the dial-back repeater terminating in this set of bank contacts.

In case the dial-back repeater terminating in this set of bank contactsis in use, then ground will be connected to the release conductor |6|whereupon a circuit may be traced for short-circuiting the switchingrelay |06 as follows: from grounded release trunk conductor, test wiper|3|, armature |23 and back contact, armature |25, through the winding ofswitching relay |06 to ground at armature |26. 'Ihe switching relay |06is prevented from operating over this circuit and this same ground fromrelease trunk conductor extends through the interrupter springs |29 andthe winding of the motor magnet |09 to energize the magnet. Motor magnet|09 thereupon energ :es from ground engaged by the test wiper |3| andcauses the wipers to step on the decnergization thereof to engageanother set of bank contacts terminating another dial-back repeater.This stepping operation continues as long as test Wiper |3| encounters agrounded bank contact.

As soon as the test wiper |3| engages a bank contact having no groundpotential thereon then the switching relay |06 energizes in series withthe marginal stepping relay |09 as follows: ground by way of armature|26 and front contact, winding of switching relay |06, interrupterspring |29, and through the winding of stepping magnet |09 to battery.Due to the high resistance of the winding of switching relay steppingmagnet |09 is not energized in this circuit. Switching relay |06, uponenergizing, at armature 23 connects ground by way of armature |26 andtest wiper |3| to release trunk conductor |6| to make this dial-backrepeater busy to the local selectors, and at armatures |22 and |24 andback contacts disconnects line relay |08 and at the front contactsconnects the trunk conductors |5| and |53 to trunk conductors and |12,whereupon a circuit is completed for energizing the battery feed relay306 as follows: from ground by way of the upper winding of relay 306,conductor 268, noring of battery feed relay normally closed .springscontrolled by armature 2|6,' conductor 269, and through the lower wind-306 to battery.

Relay 306, upon energizing, at armature 329 completes the energizingcircuit for trunkV reversing relay 30|, and at armature 330 completesthe circuit for energizing hold relay 302 and ring relay- 304, aspreviously described. At armature 3|3, relay 302 grounds the testconductor |6| by way of the busy key springs 334, conductor 26|, and thelower winding of yimpedance 201 to hold the switching relay |06`in theincoming lineswitch in operated position after the release relay |01deenergizes which it does shortly after the release of line relay |00.This ground on release trunk conductor |6| extends through wiper |3|,armature |23 and front contact to switching relay |06.

Line relay |00 deenergizes in response to the operation of switchingrelay |06, and at armature |20 opens the circuit to release relay |01and at armature |21 opens the original energizing circuit ofstepping-magnet |09. Release relay |01 in addition to being slow tooperate is likewise slow to release and therefore ground at armature |26is not removed from the winding of switchingjrelay |.06until ground issent back over test conductor |6I, as previously described.

Relay 302 also at armatures 3|5 and 3|6 prepares 4the circuit aspreviously described for operating the test relay 303 in case the wipersof the switch associated with the dial-back repeater are in engagementwith an idle trunk or complete the circuit for energizing the marginalstepping magnet 391 in case the test wiper 343 engages a grounded bankcontact indicating that this particular toll trunk is busy. Since thisoperation is the same as previously described it is not thoughtnecessary to give the detailed opera-V tions thereof. When test relay'303 energizes in response to the associated switch engaging an idle tolltrunk test relay 303 energizes and at armature 3|0 connects thering-back tone to the calling subscriber over the following circuit:from interrupted generator connected to the multiple connected bankcontacts accessible to wiper 340 through the ring-back condenser,armature 3|3, conductor 263, armature 2 I 5, conductor |10, wiper |30,front contact and armature |22, armature H8, conductor |53, tothedistant automatic exchange.

At armature 320, relay 303 connects ground by way of armature 22,conductor 213, and armature 3|5 to test wiper 343 to ground conductor362 thereby marking this toll trunk busy to other dial-back repeaters.Test relay 303 also at armature 3|9 locks itself in the same manner aspreviously described. At armature 3|1 relay 303 connects the highresistance common relay 31| in series with the lower winding ofswitching relay 305 and the winding of `stepping magnet 301. Relay 31|alone energizes over this circuit to cause the operation of the A. C.relay 216 which in turn at armature 315 completes the energization ofrelay 314. After an interval relay 314 connects ground to armature 313and conductor 310 whereupon the switching relay 305 is energized -aspreviously described. Switching relay 305 therefore energizes a shorttime after the energization of test relay 303 and at armatures 326 and33| connects generator out over the toll trunk conductors to signal thetoll operator.

Slow-to-release relay 304 deenergizes shortly after the operation ofswitching relay 305 toidisconnect ringing current and connect the tolltrunk to the windings of differential relay 2|0 and line relay 209.

When the toll operator answers the splash of ringing current, line relay209 energizes and at armature. 239 completes a circuit for energizingrelay 208. Relay 208 at armature 236 grounds the release trunk conductor|6| through the lower winding of impedance 201, at armature 231completes the circuit through the lower winding of reversing relay 20|,and at armature 238 grounds conductor 214 to hold the test relay 303 inoperated position. Relay 20| energizes and reverses battery back to thecalling distant automatic exchange at armatures 2|6 and 2|8, opens thering-back circuit at armature 2|5, and at amature 2|3 completes acircuit for the timing relay 202. Relay 202 orates and vibrates itsweighted spring 220, whereupon slowto-operate relay 206 is energizedafter a predetermined time. The circuits for operating relays 209, 206,20|, and 202 and 206 are the same as previously described andhave nottherefore been traced in detail. l

A talking circuit is now completed between the distant automaticsubscriber and the toll -operator as follows: trunk conductors |5| and|53, armatures ||8 and |2| and their back contacts, armatures |22 and|24 and front contacts, wipers |30 and |32, conductors |10 and |12,armatures 230 and 23|, armature 233, condensers C3 and C2, conductors266 and 261, armatures 3|2 and 3|| and front contacts, resting contactsand armatures 323 and 322, armatures 33| and 326, wipers 342 and 34|,and by way of the toll trunk conductors 36| and 360 to the tolloperator. Talking battery to the toll operator is furnished through thewindings of line relay 209 while talking battery through the windings ofrelay 306 is furnished to the distant automatic subscriber.

The toll operator may extend the call to a distant exchange or may callback through the dial-back switches in this local exchange bymomentarily unbalancing the line to operate differential relay 2|0andthereafter dial the local subscribers number to cause the operationof the dial-back lineswitch, the local selector and connector tocomplete the connection to the desired local line in the same manner aspreviously described. The talking circuit between the distant callingsubscriber and the local called subscriber extends over the trunkconductors |5| and |53, conductors |10 and |1| to armatures 230 and 23|,as previously traced, and thence by way of condensers C and C|, armature232 and back contact, armatures 249 and 250, conductors 216 and 216 andthrough the dial-back lineswitch, local selector, and local connector tothe called local subscribers line. After completing the connection overthe dial-back lineswitch, the local selector and connector, and thecalled subscriber has answered, the toll operator may disconnect andfree her toll trunk for other uses in the same manner as previouslydescribed. After conversation, and responsive to the distant callingsubscriber and the local called subscriber replacing their receivers thedial-back lineswitch, selector and connector in the local exchange andthe dial- .back repeater are released in the same manner as previouslydescribed when the calling subscriber opens the circuit to relay 306.When the dialin response to viously described. At armature 248 relay 2|2back repeater has released ground is removed from conductor |6|, therebyopening the circuit of switching relay |06. The removal of ground fromrelease trunk conductor |6| alsoI opens the circuit through reversingrelay whereupon the latter relay at armature ||2 disconnects ground fromrelease trunk conductors |52 and |51 to again mark this outgoingrepeater as being idle. The restoration of the switching relay |06 againprepares the incoming lineswitch for use on further incoming calls overthis trunk conductor.

In case the toll operator dials the wrong number, if a dead number isencountered, or if for some other reason the toll operator is unable tocomplete the desired connection she may release the dial-back switchesby momentarily grounding both conductors 360 and 36| to operate thedifferential relay 2|0 a second time. In order to describe thisoperation it will be assumed that the dial-back lineswitch in Fig. 6 andthe local selector in Fig. have been operated and for some reason clueto wrong dialling or otherwise the desired connection cannot becompleted. In

. the dial-back repeater in Figs. 2 and 3 it will be remembered thatcertain relays will be operated at this time before the called partyanswers, namely: relays 20|, 202, 206, 208, 209, 2||, 2|2, 302, 3|3,305, and 306. Now when the toll operator grounds the toll conductors 360and 36| differential relay 2|0 is again operated in the same manner aspreviously described. Since relays 2|| and 2| 2 are operated at thistime the operation of armature 24| by diierential relay 2|0 completes acircuit through the upper Windings of relays 2|| and 2|2 as follows:from grounded armature 239 and front contact, armature 24|, armature245, armature 244 and front contact through the upper winding of relay2|| and by way of armature 241 through` the upper winding ofdifferential dial-back relay 2| 2. The circuit traced through the upperwinding of relay 2|| malntains this relay in energized position, whilethe circuit through the upper differential winding of dial-back relay2|2 causes the differential dial-back relay 2|2 to deenergize, since theupper and lower windings now oppose each other. At armatures 241 and 248relay 2|2 simultaneously opens the circuit through both its windings andin addition at armature 248 opens the circuit through the lower windingof relay 2| I which relay, however, at this time is held energizedthrough s upper Winding alone. At armatures 249 and 250 relay 2|2 opensthe loop extending to the dial-back lineswitch and local selector andconnector to cause these switches to release in the same manner aspreviously described. The toll operator now removes the unbalancingground condition from conductors 360 and 36|, whereupon differentialrelay 2|0 deenergizes. At armature 24| relay 2|0 opens the circuitthrough the upper winding of relay 2| I, whereupon this relay nowdeenergizes. Relay 2|| at armature 243 completes the original energizingcircuit of trunk reversing relay 30| which thereupon operates andreverses battery to the toll operator as previously described.

The toll operator may now reoperate the dialback lineswitch by againconnecting ground to both conductors 360 and 36| to reenergize thediiierential relay 2|0. T'he operation of relay 2 I0 at armature 24|causes the operation of relay 2|2 which at armatures 249 and 250 closesa loop circuit to the dial-back lineswitch to cause it to plunge andseize an idlelocal selector, as precompletes the circuit for operatingrelay 2|| when the short circuiting ground is removed by thedeenergization of the differential relay 2|0 as previously described.The operation from here on is the same as previously described.

From the foregoing it will be seen that when the toll operator completeseither incoming or outgoing calls between the local and distantautomatic subscribers lines, the toll operator is disconnected fromthese established connections and it is therefore desired to provide thetoll operator with some means for ascertaining the idle or busycondition of the trunk lines connecting the distant and local automaticexchanges. The monitor selector shown in Fig. 4 is therefore provided inorder for the toll operator to determine thc idle or busy condition ofthe trunk lines connecting the two automatic ex changes. Assuming nowthat the toll operator Wants to test the idle or busy condition of thetrunk lines connecting the two automatic exchanges, then the tolloperator will select one of her toll trunks extending to the localautomatic exchange and in this case it will be further assumed that thetrunk conductors 380 and 36| are the conductors of the trunk lineselected. 'I'he toll operator in selecting this trunk line throws abridge across the conductors 360 and 36| thereby completing a circuitfor energizing line relay 620 of the incoming toll lineswitch asfollows: from ground through springs 624, conductor 36|, through thetoll operators bridge, conductor 360, springs 623 and through thewinding of line relay 620 to battery. Since the operation of theincoming toll lineswitch is similar to both the dial-back lineswitch andlocal lineswitch, the operation of line relay 620 causes the plungercoil 626 to operate and select an idle local selector. Assuming furtherthat the local selector in Fig. 5 is the selector seized by the plungingof the incoming toll lineswitch. When the toll operator hears dial tonetransmitted from the seized selector, she will operate the localselector opposite the eighth level to seize the monitor selector in Fig.4 in the same manner as previously described.

When the local selector switches through in response to' the operatingof switching relay 501, line relay 406 in the monitoring selector isenergized over the following circuit: from ground through the lowerWinding of line relay 406, normally closed springs controlled byarmature 425, conductor 462, wiper 542, front contact and armature 530,conductor 563, contact 635, conductor 36|, through the bridge at thetoll operators position, conductor 360. springs 63|, conductor 560,armature 526 and front contact, wiper 540, conductor 460, normallyclosed contacts controlled by armature 423, and through the upperwinding of line relay 406 to battery. At armature 428 line relay 406completes the circuit for the slowto-release relay 405. At armature 426relay 405 connects ground to release trunk conductor 46| to maintain thepolarized switching relay 501 and the pull-down coil 626 in operatedposition to maintain the local selector and incoming toll line switch inoperated position, and at armature 421 connects ground to armatures 4|4and 4 I9.

The toll operator now dials the digit 1 in order to supervise the rsttrunk line connecting the two automatic exchanges. In response to thisdigit, or digit 1, line relay 406 deenergizes and at armature 428kcompletes the circuit for energizing slow-to-release relay 403 asfollows: from ground by way of armature 428 and back contact, armature429, and through the winding of slow-torelease relay 403 to battery. Atarmature 42| relay 403, upon energizing, opens the circuit of reversingrelay 404, and at armature 422 completes a circuit through the upperwinding of trunk No. I relay 402 to operate this relay in its first stepto close its X contact at armature 4|9. This circuit may be traced asfollows: from ground by way of armature 428 and back contact, amature429, armature 422, armature 4|8l and back contact, and through the upperwinding of relay 402 to battery. Relay 402 operates its armature 4|9 tocomplete a holding circuit for its upper winding and at the same timeshort circuits its lower winding from ground at armature 421 to groundat armature 428. When line relay 406 energizes after this impulse,ground at armature 428 is removed from the winding of series relay 403and the windings of relay 402, whereupon the two-step relay 402energizes in itssecond step over the following circuit: from ground byway of armature 421, armature 4|9, through the lower winding of two-steprelay 402 land through the upper winding to battery. Relay 402 operatesits remaining armatures and at armatures 4|6 and 420 connects thetalking conductors 460 and 462 by way of armatures 4| I and 4|5 and backcontacts to conductors |5| and |53 extending to the distant automaticexchange. At armature 4|1 two-step relay 402 prepares a point in thecircuit to the reversing relay 404. At

" armature 4|8 relay 402 preparesa point in the circuit for energizingtrunkk No. 2 relay 40|. Shortly after the impulsing period, series relay403 deenergizes and at the normally closed springs controlled byarmature 42| completes the circuit for energizing the reversing relay404 in case ,the rst trunk line to the distant automatic exchange isbusy. In this case ground'will be connected to test conductor |52,-thereby completing the energizing circuit for relay 404; from groundedconductor |52, back contact and armature 4|2, armature 4|?, normallyclosed springs controlled by armature 42|, and through the winding ofreversing relay 404 to battery. At armature 424 relay 404 prepares alocking circuit for itself and at armatures 423 and 425 reverses batteryfrom the windings of the line relay 406 back over the toll trunkconductors in order to advise the o`perator that the first trunk line isbusy. If desired, the toll operator may converse with the subscribers inthe established connection or may camp on this connection until suchtime as. the subscribers release whereupon groundis removed fromconductor |52 to cause the deenergization of reversing relay 404 whichthereupon again reverses battery back over the talking conductor to thetoll operator advising such operator that the first trunk line is nowidle and may be used on other calls.

If desired the toll operator may transmit .another impulse to line relay406 to test the idle or busy condition of the second trunk line. Inresponse to this impulse line relay 406 again de` energizes and againcompletes the circuit for series relay 403 and at the same timecompletes the circuit for energizing two-step relay 40| in its rst stepto operate armature 4|4. The circuit. for operating relay 40| in its rststep may be traced as follows: from ground by way of armature 428 andback contact, armature 429, armature 422, armature 4|8 and frontcontact, armature 4|3 and back contact, through the upper winding ofrelay 40| to battery, At this time relay 40| operates only its armature4|4 to complete a short circuit around its lower winding extending fromground at amature 421 and ground at armature 428. When line relay 406energizes after this impulse, the circuit to series relay 403 is openedand the short circuit around the lower winding of two-step relay 40| isremoved with the result that relay 40| operates through its second stepto operate its remaining armatures. When series relay 403 energized inresponse to the second impulse, said relay at armature 42| completed thelocking circuit for reversing relay 404 and at armature 422 completedthe previously traced circuit for relay 40|. At armature 4|2 relay 40|,upon operating through its second step, disconnects' test conductor |52of the first trunk and connects up test conductor |52' of the secondtrunk and at armatures 4|| and 4|5 disconnects the talking conductors ofthe first trunkand connects up the talking conductors of the secondtrunk. At armature 4|3 relay 40| opens the original energizing circuitto upper winding of relay 40| and transfers the impulsing circuit to asucceeding relay in case there are more than two trunks connecting thetwo automatic exchanges. Shortly after the second impulse transmitted bythe toll operator, series relay 403 deenegizes and at armature 42|connects the reversing relay 404 to the test conductor |52'. In case thesecond trunk is busy ground on conductor |52' will maintain thereversing relay energized to maintain the reversed battery connection tothe toll operator, thereby advising the toll operator that the secondtrunk is likewise busy. In case the second trunk line is not busy thenno circuit is completed for reversing relay 404 with the result thatrelay 404 deenerglzes and restores normal talking connections to thetoll trunk thereby advising the operator that the second toll trunk isidle. From the foregoing it is therefore seen that by use of the monitorselector the toll operator is enabled to connect with the trunk linesconnecting the two automatic exchanges regardless of their idle or busycondition and may converse thereover in case the trunk lines are 1n use.

Incoming toll calls from the toll switching center to local automaticsubscribers are handled through the incoming toll lineswitch and thelocal selector and connector, while incoming-toll calls from the tollswitching center to the distant automatic exchanges are handled by theincoming line switch, local selector, and the outgoing repeater to thedistant automatic exchange. The operation of the local selector andoutgoing repeater is the same as previously described, except in thiscase no dial-back repeater is included ln the circuit as the localselector when used by the toll operator connected with the 'outgoingrepeaters direct.

Having described the invention, what is considered to be new and isdesired to be protected by Letters Patent is set forth in the followingclaims.

What is claimed is:

1. In a telephone system, a distant exchange, a local exchange, and atoll exchange, trunk lines connecting the distant and local exchanges,dialback repeaters in the local exchange, a hunting switch individual toeach said trunk line having access to said repeaters, toll trunk linesconnecting the local and toll exchanges, a selecting switch individualto each said repeater having access to said toll trunk lines, automaticsubscribers lines terminating in said local exchange, local

